What is Q265GNH?

Q265GNH is a high-weathering structural steel defined in GB/T 4171, offering excellent atmospheric corrosion resistance with a minimum yield strength of 265 MPa. The "GNH" designation indicates "high weathering" (Gao Nai Hou), meaning enhanced corrosion resistance compared to standard weathering steels. With the addition of alloying elements such as copper, chromium, nickel, and phosphorus, it forms a stable, protective rust layer over time—significantly reducing the need for painting and lowering lifecycle maintenance costs. In real-world use, it's a reliable, durable choice for railway vehicles, containers, bridges, and outdoor steel structures requiring superior atmospheric corrosion resistance.

📄 GB/T 4171—2008 🌱 High Weathering (GNH) 🔩 Weldable / Riveted / Bolted Connections
📊 7.1 Chemical Composition (Ladle Analysis)
Grade C Si Mn P S Cu Cr Ni Other Elements
Q265GNH ≤0.12 0.10~0.40 0.20~0.50 0.07~0.12 ≤0.020 0.20~0.45 0.30~0.65 0.25~0.50 (a,b)
📌 Footnotes Explanation:
(a) Micro-alloys: Nb(0.015%~0.060%), V(0.02%~0.12%), Ti(0.02%~0.10%), Alt≥0.020%; at least one element reaches the lower limit
(b) May contain Mo≤0.30%, Zr≤0.15%
(c) Nb+V+Ti total ≤0.22% (for Q415NH~Q550NH)
(d) By agreement, S content can be ≤0.008%
(e) By agreement, Ni lower limit may be waived
(f) By agreement, C content can be ≤0.15% (for Q235NH/Q295NH)

🔹 7.1.2 Permissible deviation for finished product chemical composition shall comply with GB/T 222.

🔹 7.2 Melting Method — Steel shall be made by converter or electric furnace, killed steel. Method at supplier's option unless specified.

🔹 7.3 Delivery Condition — Hot-rolled products delivered as-rolled, controlled-rolled or normalized; cold-rolled products generally annealed.

⚙️ 7.4 Mechanical Properties & Process Performance
Grade Thickness (mm) Lower Yield Strength (MPa) Tensile Strength (MPa) Elongation A% 180° Bend Test
Mandrel Diameter
Q265GNH ≤3.5 265 ≥410 27 a
📌 Mechanical Property Footnotes:
Note 1: "a" = steel thickness (mandrel diameter in bend test = a for Q265GNH)
Note 2: When yield point is not obvious, Rp0.2 may be used
Note 3: For thickness >3.5mm, mechanical properties subject to agreement
🔹 Impact Properties (Table 5) — Q265GNH available quality grades: Grade A (+20°C ≥47J); Grade B (0°C ≥34J); Grade C (-20°C ≥34J); Grade D (-40°C ≥27J).
7.4.2.1 By agreement, high weathering steel may be exempt from impact test.
7.4.2.2 Average of three specimens; one single value may be lower but not less than 70% of specified value.
7.4.2.3 Impact test required for thickness ≥6mm or diameter ≥12mm; sub-size specimens require proportional reduction.
Note 4: By agreement, average impact energy can be ≥60J
🔍 7.5 Additional Requirements
Grain Size — Shall be not less than Grade 7, with uniformity within three adjacent grade levels.
Non-metallic Inclusions (GB/T 10561 Method A): A≤2.5, B≤2.0, C≤2.5, D≤2.0, DS≤2.0.
🧪 7.6 Surface Quality
  • 7.6.1 No cracks, blisters, folds, bubbles, inclusions or laminations. Removal depth ≤ half thickness tolerance.
  • 7.6.2 Hot-rolled surfaces may have minor defects that do not affect usability, provided minimum thickness is maintained.
  • 7.6.3 Cold-rolled sheets/strips may have slight scratches, oxidation color, light yellow film, local pitting, marks within tolerance.
  • 7.6.4 Strips may be delivered with defects, but defective portion ≤8% of total length.
🌿 Atmospheric Corrosion Resistance Assessment (Appendix C & D)
📘 Appendix C · Protective Patina Layer
Corrosion resistance depends on alloying elements (Cu, Cr, Ni, P) forming a dense rust layer. Alternating wet-dry cycles aid patina stability.
🧪 Appendix D · Corrosion Resistance Index (I)
I = 26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P) - 7.29(%Cu)(%Ni) - 9.10(%Ni)(%P) - 33.39(%Cu)²
Index ≥6.0 indicates excellent weathering performance.

💡 Based on ISO 5952:2005 Appendix A and ASTM G101 methods. Minimum acceptable corrosion index shall be agreed between supplier and purchaser.

📚 Grade Comparison & Available Dimensions (Table 2)
GB/T 4171-2008 GB/T 4171-2000 TB/T 1979-2003 JIS G3125 Thickness/Diameter Range
Q265GNH Q295GNHL 09CuPCrNi-B — Plate/strip ≤3.5mm, sections —

📐 Dimensional Tolerances: Hot-rolled plate/strip per GB/T 709, cold-rolled per GB/T 708.

* Technical data based on GB/T 4171—2008, fully covering all requirements of Chapter 7 (7.1~7.6.4) and appendices.